The role of modal auxiliaries is no less important than the helping and linking auxiliary verbs in expressing the possibility, advice, wish, and necessity. Among all the modal auxiliary verbs, modal verbs for possibility have greater role in the english grammar.
Can, could, and may are mainly used to indicate ability, possibility, and permission. We know that these are commonly used modal auxiliaries in our daily interaction.
The first and foremost role of this auxiliary is to express ability to do something. It is used to for both negative and positive purposes. For this, ‘could’ is the past form of ‘can’ to carry the assigned role.
Second, can is also used for permission but to grant permission. Instead, ‘may’ is the most applicable auxiliary to ask for permission.
Unlike helping and linking auxiliaries, it doesn’t change its form according to the number and person of the subject of given sentence.
•Students of tenth class can easily understand the basic mathematical calculations.
•Generally, tenth class students cannot write a thesis statement.
•He can ride a bike but cannot drive a car.
•Man can invent advanced technology but cannot replace the nature.
•Agriculture is the most primitive occupation. It is started prior to the iron age civilization. Anyone can learn it without difficulty.
Usually, it is preferred to express past ability, milder possibility, and formal request but less polite than ‘would.’
‘Can’ indicates present ability; whereas, ‘could’ is used for past ability. For possibility, ‘may’ expresses stronger possibility compare to ‘could and might.’
In order to make a polite request, ‘would’ deserves priority compare to could auxiliary. Obviously, ‘would’ is more polite than ‘could.’
•It was a hasty desicion. He could wait for a better opportunity. Unfortunately, it couldn’t happen.
•Had they agreed to go for the negotiations to solve the border disputes, the devastating war could have been averted.
‘Could have’ is also used to express irreversible missed opportunity.
Here, the most important use of this auxiliary is to indicate possibility in future without future auxiliary; and to ask for permission but more polite in nature.
Compare to other modal auxiliary verbs, ‘may’ deserves priority in terms of possibility and permission.
•It may rain or may not be as we know that this is the same situation that we have been witnessing since a week.
•May I use your bike to drop my younger brother for school ?
•Today, he may be late due to heavy rain.
•In this summer, the rate of energy consumption may rise sharply compare to earlier season. For this, growing demand and impact of climate change may be the potential reasons.
•The crisis of food security may escalate in the coming future as the more land is being diverted for the other crops.
These are some useful examples of “can could and may.” Definitely, all these may help you to improve your vehicle of communication
In conclusion, you know that there is a lot of confusion in terms of correct use of modal auxiliary verbs just because of the ambiguous nature of some of the modals.
Here, many modal auxiliaries express same meaning but with varying degrees. Hence, we need to use them as per theirs major role. Otherwise, a lot of confusion may arise in our mind.